C++ 从内存写入时,有时会损坏TGA文件
当我从内存中写入包含从tga文件加载到tga文件的RGBA像素数据的图像缓冲区时,有时会观察到一种奇怪的行为 图像缓冲区从TGA文件加载,算法从该线程窃取和改编: 我从这个地址窃取并改编的写作方法: 下面是一个最小的可编译示例,其中tileA.tga被正确地保存回光盘作为tileA_new.tga,但是TileB_new.tga被破坏了图形看起来很奇怪,带有假像素!为什么TileB_new.tga坏了 这两个源tga文件是不同的,但它们可以在gimp和irfanview中正确查看,我仔细检查了加载算法。这是可行的,因为当我用OpenGL将两个加载的瓷砖的图像缓冲区渲染到屏幕上时,它们看起来是正确的!但将原始缓冲区写入磁盘的行为不同,为什么?我在十六进制编辑器中比较了源tga文件的头,但它们是相等的。此外,写入的tga文件具有相同的标题。 我能看到的是,tileB.tga的大小是tileA.tga的5倍,但这似乎是正确的,因为gimp/irfanview显示的是正确的。也许你能看到我在这里犯的错误 //一个包含两个tga文件的小型visual studio项目可在此处下载 最简单的例子:C++ 从内存写入时,有时会损坏TGA文件,c++,file-writing,tga,C++,File Writing,Tga,当我从内存中写入包含从tga文件加载到tga文件的RGBA像素数据的图像缓冲区时,有时会观察到一种奇怪的行为 图像缓冲区从TGA文件加载,算法从该线程窃取和改编: 我从这个地址窃取并改编的写作方法: 下面是一个最小的可编译示例,其中tileA.tga被正确地保存回光盘作为tileA_new.tga,但是TileB_new.tga被破坏了图形看起来很奇怪,带有假像素!为什么TileB_new.tga坏了 这两个源tga文件是不同的,但它们可以在gimp和irfanview中正确查看,我仔细检查了加
因为我的评论似乎已经解决了问题,见上文。我将在这里展开 在至少有微软CRT的Windows上,以文本模式写入文件和以二进制模式写入文件之间存在显著差异 具体而言,任何与“\n”匹配的字符都将扩展为两个字符序列\r\n。此外,某些函数应用MB和unicode字符之间的转换。有关更多信息,请访问fopen上的MSDN文档,网址为: 因此,在读取/写入非文本数据时,请确保将rb或wb标志传递给fopen(视情况而定)
在Posix系统上,这一考虑不适用,但明确您的意图仍然是一种良好的做法。以二进制文件而不是文本文件的形式写入,否则换行符将在Windows上展开。哦,天哪,哦,是的!我调试了几个小时,但这是一个简单的解决方案!详细解释请参见Thanx。
#include <vector>
#include <fstream>
//special-sausage for microsoft
#ifdef _MSC_VER
#pragma warning(disable:4996)
#endif
//=========================================
// Code for loading a TGA-file
//=========================================
typedef union PixelInfo
{
std::uint32_t Colour;
struct
{
std::uint8_t R, G, B, A;
};
} *PPixelInfo;
class Tga
{
private:
std::vector<std::uint8_t> Pixels;
bool ImageCompressed;
std::uint32_t width, height, size, BitsPerPixel;
public:
Tga(const char* FilePath);
std::vector<std::uint8_t> GetPixels() { return this->Pixels; }
std::uint32_t GetWidth() const { return this->width; }
std::uint32_t GetHeight() const { return this->height; }
std::uint32_t GetBitsPerPixel() const { return this->BitsPerPixel; }
bool HasAlphaChannel() { return BitsPerPixel == 32; }
};
Tga::Tga(const char* FilePath)
{
std::fstream hFile(FilePath, std::ios::in | std::ios::binary);
if (!hFile.is_open()) { throw std::invalid_argument("File Not Found."); }
std::uint8_t Header[18] = { 0 };
std::vector<std::uint8_t> ImageData;
static std::uint8_t DeCompressed[12] = { 0x0, 0x0, 0x2, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0 };
static std::uint8_t IsCompressed[12] = { 0x0, 0x0, 0xA, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0 };
hFile.read(reinterpret_cast<char*>(&Header), sizeof(Header));
if (!std::memcmp(DeCompressed, &Header, sizeof(DeCompressed)))
{
BitsPerPixel = Header[16];
width = Header[13] * 256 + Header[12];
height = Header[15] * 256 + Header[14];
size = ((width * BitsPerPixel + 31) / 32) * 4 * height;
if ((BitsPerPixel != 24) && (BitsPerPixel != 32))
{
hFile.close();
throw std::invalid_argument("Invalid File Format. Required: 24 or 32 Bit Image.");
}
ImageData.resize(size);
ImageCompressed = false;
hFile.read(reinterpret_cast<char*>(ImageData.data()), size);
}
else if (!std::memcmp(IsCompressed, &Header, sizeof(IsCompressed)))
{
BitsPerPixel = Header[16];
width = Header[13] * 256 + Header[12];
height = Header[15] * 256 + Header[14];
size = ((width * BitsPerPixel + 31) / 32) * 4 * height;
if ((BitsPerPixel != 24) && (BitsPerPixel != 32))
{
hFile.close();
throw std::invalid_argument("Invalid File Format. Required: 24 or 32 Bit Image.");
}
PixelInfo Pixel = { 0 };
int CurrentByte = 0;
std::size_t CurrentPixel = 0;
ImageCompressed = true;
std::uint8_t ChunkHeader = { 0 };
int BytesPerPixel = (BitsPerPixel / 8);
ImageData.resize(static_cast<size_t>(width) * static_cast<size_t>(height) * sizeof(PixelInfo));
do
{
hFile.read(reinterpret_cast<char*>(&ChunkHeader), sizeof(ChunkHeader));
if (ChunkHeader < 128)
{
++ChunkHeader;
for (int I = 0; I < ChunkHeader; ++I, ++CurrentPixel)
{
hFile.read(reinterpret_cast<char*>(&Pixel), BytesPerPixel);
ImageData[CurrentByte++] = Pixel.B;
ImageData[CurrentByte++] = Pixel.G;
ImageData[CurrentByte++] = Pixel.R;
if (BitsPerPixel > 24) ImageData[CurrentByte++] = Pixel.A;
}
}
else
{
ChunkHeader -= 127;
hFile.read(reinterpret_cast<char*>(&Pixel), BytesPerPixel);
for (int I = 0; I < ChunkHeader; ++I, ++CurrentPixel)
{
ImageData[CurrentByte++] = Pixel.B;
ImageData[CurrentByte++] = Pixel.G;
ImageData[CurrentByte++] = Pixel.R;
if (BitsPerPixel > 24) ImageData[CurrentByte++] = Pixel.A;
}
}
} while (CurrentPixel < (static_cast<size_t>(width) * static_cast<size_t>(height)));
}
else
{
hFile.close();
throw std::invalid_argument("Invalid File Format. Required: 24 or 32 Bit TGA File.");
}
hFile.close();
this->Pixels = ImageData;
}
//=========================================
// code for writing a TGA-file
//=========================================
void writeTGA(const std::string &refFile, Tga &refTGA)
{
unsigned short width = static_cast<unsigned short>(refTGA.GetWidth());
unsigned short height = static_cast<unsigned short>(refTGA.GetWidth());
unsigned char bitsPerPixel = static_cast<unsigned char>(refTGA.GetBitsPerPixel());
unsigned char bitsAlphaChannel = (bitsPerPixel == 32 ? 8 : 0);
FILE * fptr = fopen(refFile.c_str(), "w");
putc(0, fptr);
putc(0, fptr);
putc(2, fptr); /* uncompressed RGB */
putc(0, fptr); putc(0, fptr);
putc(0, fptr); putc(0, fptr);
putc(0, fptr);
putc(0, fptr); putc(0, fptr); /* X origin */
putc(0, fptr); putc(0, fptr); /* y origin */
putc((width & 0x00FF), fptr);
putc((width & 0xFF00) / 256, fptr);
putc((height & 0x00FF), fptr);
putc((height & 0xFF00) / 256, fptr);
putc(bitsPerPixel, fptr); /* 24/32 bit bitmap */
putc(bitsAlphaChannel, fptr); /* When 32 bit, write 8, else 0 */
auto pixelData = refTGA.GetPixels();
for (size_t i = 0; i < static_cast<size_t>(width) * static_cast<size_t>(height) * (bitsPerPixel/8); i += (bitsPerPixel/8))
{
unsigned char r = pixelData[i];
unsigned char g = pixelData[i + 1];
unsigned char b = pixelData[i + 2];
unsigned char a = (bitsAlphaChannel == 8 ? pixelData[i + 3] : 0);
putc(b, fptr);
putc(g, fptr);
putc(r, fptr);
if (bitsAlphaChannel == 8)
putc(a, fptr);
}
fclose(fptr);
}
//=========================================
// main
//=========================================
int main()
{
Tga oTgaA("tileA.tga");
writeTGA("tileA_new.tga", oTgaA); // works correct as aspected
Tga oTgaB("tileB.tga");
writeTGA("tileB_new.tga", oTgaB); // graphic-file has artefacts, why?
}